Oily cold water fish, such as salmon, trout, herring, and tuna are the source of dietary marine omega-3 fatty acids, with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) being the key marine derived omega-3 fatty acids. Omega-3 fatty acids have previously been shown to improve insulin sensitivity and glucose tolerance in normoglycemic men and in obese individuals. Omega-3 fatty acids have also been shown to improve insulin resistance in obese and non-obese patients with an inflammatory phenotype. Lipid, glucose, and insulin metabolism have been shown to improve in overweight hypertensive subjects through treatment with omega-3 fatty acids. Omega-3 fatty acids (EPA/DHA) have also been shown to decrease triglycerides and to reduce the risk for sudden death caused by cardiac arrhythmias in addition to improve mortality in patients at risk of a cardiovascular event. Omega-3 fatty acids have also been taken as dietary supplements part of therapy used to treat dyslipidemia, and anti-inflammatory properties. A higher intake of omega-3 fatty acids lower levels of circulating TNF-α and IL-6, two of the cytokines that are markedly increased during inflammation processes (Chapkin et al, Prostaglandins, Leukot Essent Fatty Acids 2009, 81, p. 187-191; Duda et al, Cardiovasc Res 2009, 84, p. 33-41). In addition, a higher intake of omega-3 fatty acids has also been shown to increase levels of the well-characterized anti-inflammatory cytokine IL-10 (Bradley et al, Obesity (Silver Spring) 2008, 16, p. 938-944).
Both DHA and EPA are characterized as long chain fatty acids (aliphatic portion between 12-22 carbons). Medium chain fatty acids are characterized as those having the aliphatic portion between 6-12 carbons. Lipoic acid is a medium chain fatty acid found naturally in the body. It plays many important roles such as free radical scavenger, chelator to heavy metals and signal transduction mediator in various inflammatory and metabolic pathways, including the NF-κB pathway (Shay, K. P. et al. Biochim. Biophys. Acta 2009, 1790, 1149-1160). Lipoic acid has been found to be useful in a number of chronic diseases that are associated with oxidative stress (for a review see Smith, A. R. et al Curr. Med. Chem. 2004, 11, p. 1135-46). Lipoic acid has now been evaluated in the clinic for the treatment of diabetes (Morcos, M. et al Diabetes Res. Clin. Pract. 2001, 52, p. 175-183) and diabetic neuropathy (Mijnhout, G. S. et al Neth. J. Med. 2010, 110, p. 158-162). Lipoic acid has also been found to be potentially useful in treating cardiovascular diseases (Ghibu, S. et al, J. Cardiovasc. Pharmacol. 2009, 54, p. 391-8), Alzheimer's disease (Maczurek, A. et al, Adv. Drug Deliv. Rev. 2008, 60, p. 1463-70) and multiple sclerosis (Yadav, V. Multiple Sclerosis 2005, 11, p. 159-65; Salinthone, S. et al, Endocr. Metab. Immune Disord. Drug Targets 2008, 8, p. 132-42).
Statins have been used widely to lower low-density cholesterol (LDL-C), a key risk factor in cardiovascular disease. Because of their ability to inhibit 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, these agents can essentially block the rate-limiting step in the cholesterol biosynthesis in the liver. After extended clinical use, statins have been shown to be safe and effective for both primary prevention of coronary heart disease and secondary prevention of coronary events. More recently, there is increasing evidence that indicates that statins can exert beneficial effects on inflammatory processes. For instance, after treatment with atorvastatin, a DNA microarray analysis of human peripheral blood lymphocytes showed a significant decrease in the gene expression of six cytokines (IL-6, IL-8, IL-1, PAI-1, TGF-b1, TGF-b2) and five chemokines (CCL2, CCL7, CCL13, CCL18, CXCL1) (Wang et al, Biomedicine & Pharmacotherapy 2011, 65, p. 118-122). The high mobility group box-1 (HMGB1) has recently been implicated as a potential pro-inflammatory cytokine that could play a critical role in endothelial dysfunction and atherosclerosis. Treatment of endothelial cells with atorvastatin has been shown to markedly suppress HMGB1-induced Toll like receptor 4 (TLR4) expression, NF-κB nuclear translocation and DNA binding (Yang et al, Molecular & Cellular Biochemistry 2010, 345, p. 189-195).
Because of the ability of statins and omega-3 fatty acid to act on the NF-κB axis, a synergistic activity would provide a great benefit in treating a number of metabolic diseases. Synergistic activity can be achieved through a fatty acid statin conjugates which are comprised of a statin covalently linked to a fatty acid to form a plasma stable molecular entity. However, once delivered inside cells, intracellular enzymes hydrolyze the fatty acid statin conjugate into the individual components. In addition, a fatty acid statin conjugate can also display synergistic activity on the various lipid synthesis pathways that cannot be replicated by administering the individual components (i.e. omega-3 fatty acid alone and statin alone) or a combination of the individual components not covalently linked. For instance, the statin drug class has been used extensively in the clinic to lower cholesterol. However, statin treatment has been shown to significantly increase the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9) (Dubuc et al Arterioscler. Thromb. Vasc. 2004, p. 1453-1459). The increased level of PCSK9 could essentially counteract some of the beneficial effects of statins since PCSK9 could enhance the degradation of LDL receptors, leading to higher plasma levels of LDC-C. As demonstrated herein, a fatty acid statin conjugate shows a different activity profile toward PCSK9 that cannot be replicated by administering a statin and an omega-3 fatty acid. Selective targeting to certain tissue types can enhance the overall efficacy, as well as reduce the side effects. Selective targeting of fatty acid statin conjugates to certain tissue types (such as the liver) can be carried out using omega-3 fatty acids as well as non-omega-3 fatty acids. Examples of non-omega-3 fatty acids that can be used to form covalent conjugates with statins include saturated fatty acids, omega-6 fatty acids, omega-9 fatty acids, omega-1 fatty acids, omega-7 fatty acids, omega-12 fatty acids, omega-15 fatty acids, sapienic acid, linoelaidic acid, pinolenic acid, and podocarpic acid.
The farnesoid X receptor (FXR) is a nuclear hormone receptor expressed in the liver, gall bladder, kidney, adrenal glands and intestine. Upon activation by bile acids, FXR binds to DNA as a heterodimer with the retinoid X receptor (RXR) and this binding, in turn, regulates the expression of a number of genes and proteins involved in bile acid and cholesterol homeostasis, triglyceride synthesis and lipogenesis (For reviews on FXR see: Kalaany et al Annu. Rev. Physiol. 2006, 68, p. 159-191; Zhang et al FEBS Lett. 2008, 582, p. 10-18). In addition, FXR can help maintain glucose homeostasis, possibly because of its effects on gluconeogenesis, insulin sensitization and glycogen synthesis (Zhang et al Proc. Natl. Acad. Sci. USA 2006, 103, p. 1006; Cariou et al FEBS Lett. 2005, 579, p. 4076). Activation of FXR has been shown to result in increased hepatic expression of receptors that are involved in lipoprotein clearance (VLDL receptor and syndecan-1) and increased apoC-II that coactivates lipoprotein lipase (LPL). In addition FXR activation results in decreased expression of proteins such as apoC-III and ANGPTL3 that could function as inhibitors of LPL (Lee et al Trends Biochem. Sci. 2006, 31, p. 572-580). Thus, agonists of FXR can potentially be useful in treating a number of metabolic diseases because of its ability to lower plasma triglycerides, repress hepatic lipogenesis and triglyceride synthesis, as well as increase the clearance of triglyceride-rich lipoproteins from the blood. The fatty acid FXR agonist conjugates are comprised of an FXR agonist covalently linked to a fatty acid. This fatty acid FXR agonist conjugate is stable in the plasma. However, once delivered inside cells, intracellular enzymes would hydrolyze the conjugate into the individual components. Because of the ability of FXR agonists and omega-3 fatty acids to impact the different lipid synthesis pathway, a fatty acid FXR agonist conjugate will display synergistic activity that cannot be replicated by administering the individual components or a combination of the individual components. Selective targeting to certain tissue types can enhance the overall efficacy, as well as reduce the side effects. Selective targeting of fatty acid FXR agonist conjugates to certain tissue types (such as the liver) can be carried out using omega-3 fatty acids as well as non-omega-3 fatty acids.